During the installation and maintenance of load bearing cables such as in marine applications, it is necessary to lower and/or raise cables into position. Winch assemblies must be capable of withstanding heavy loads from the weight of the cables and loads attached to the cables.
In applications which use relatively short cable lengths with small loads conventional reel winches may be used. However, for longer cable lengths with heavy loads reel winches are not suitable as they require large drums to accommodate the longer cable and may result in unacceptable loading applied to the drum. Furthermore, the reel winch may prevent the tensioning and releasing of the cable from being accurately controlled.
It is known to use linear winches in combination with a reel winch. The linear winch is used to pull the cable and maintain the tension on the cable while the reel winch reels or unreels the cable on a reel drum.
Linear winches usually comprise two gripper assemblies which clamp and pull the cable in a coordinated operation. As a first gripper assembly grips and pulls the cable a second gripper assembly allows the cable to pass freely. As the second gripper assembly grips and pulls the cable the first gripper assembly releases the cable and slides over the cable to return to its initial position. The successive holding and releasing steps of the two gripper assemblies allows the tension of the cable to be maintained as it is pulled.
U.S. Pat. No. 4,569,507 describes a traction block for a linear winch comprising an elongate frame and two clamping blocks which are mounted between lateral flanges on the frame so that a relative longitudinal movement between each movable clamping block and the adjacent flange of the frame causes a transverse movement of the respective movable clamping block. The traction block also comprises a cover plate which is detachable fixed to the traction block.
A disadvantage of this system is that the winch must be taken offline, the winch assembly dismantled and components of the winch to be removed in order to lift the cable connector clear of the winch assembly. This is time consuming and dangerous operation especially when the cable is under tension.